The present invention relates to a composite magnet of electromagnet and permanent magnet, comprising an iron core, a coil arranged to surround the outer peripheral surface of the iron core, and a permanent magnet mounted in the iron core in a manner that the magnetic pole is in agreement with the direction of magnetization of the iron core. The invention further relates to an eddy current retarder used for assisting the foot brake which is the main brake of a vehicle such as a truck, i.e., to an eddy current retarder equipped with the composite magnet of electromagnet and permanent magnet. The invention further relates to an eddy current retarder used for assisting the foot brake which is the main brake of a vehicle such as a truck, and to an eddy current retarder in which annular members made of a good conductor such as copper, a copper alloy or the like is coupled to the brake drum.
Japanese Examined Utility Model Publication (Kokoku) No. 44930/1988 discloses a composite magnet of electromagnet and permanent magnet comprising an iron core, a coil arranged to surround the outer peripheral surface of the iron core, and a permanent magnet mounted in the iron core in a manner that the magnetic pole is in agreement with the direction of magnetization of the iron core. A groove extending in the axial direction is formed in a part in the outer periphery of the iron core in the circumferential direction, the groove being formed at an intermediate portion in the axial direction or extending from one end to the other end in the axial direction. A permanent magnet is fitted into the groove.
A permanent magnet (e.g., ferrite magnet, rare-earth magnet) has a magnetic permeability smaller than that of the iron core (usually, a low-carbon iron material). In the above-mentioned composite magnet, since a permanent magnet having a low magnetic permeability is attached to a portion in the outer periphery of the iron core in the circumferential direction, the magnetic flux formed in the iron core cannot be sufficiently efficiently collected to one of the magnetic pole surfaces of the iron core when the iron core is magnetized by supplying a current to the coil. That is, since a permanent magnet having a low magnetic permeability is mounted on a portion in the outer periphery of the iron core in the circumferential direction, a portion in the outer periphery of the iron core in the circumferential direction is shut off in the direction of magnetization, the flow of magnetic flux formed in a portion of the outer periphery of the iron core is interrupted by the permanent magnet, and the magnetic flux formed in a portion in the outer periphery of the iron core is not efficiently guided as desired to one of the magnetic pole surfaces of the iron core. Further, the region of the iron core where the permanent magnet exists becomes remote from a portion of the coil in the radial direction, and the magnetic flux corresponding to the current supplied to the coil can not be efficiently generated. When the iron core is magnetized by supplying a current to the coil, therefore, the magnetic flux is not very efficiently generated in the iron core and hence, performance of the electromagnet is not utilized to a sufficient degree. Besides, since the permanent magnet is mounted on a portion of the outer periphery of the iron core in the circumferential direction thereof, it is not allowed to sufficiently increase the sectional area of the permanent magnet as desired and hence, the permanent magnet cannot be effectively utilized. Summarizing the foregoing, neither the electromagnet nor the permanent magnet is effectively utilized. Due to that neither electromagnet nor the permanent magnet is effectively utilized, the length of the electromagnet (iron core and coil) increases in the direction of magnetization, the composite magnet as a whole becomes of larger size, the weight increases, and the cost of production increases, too. The transverse sectional area of the iron core at a portion where the permanent magnet is mounted becomes considerably larger than the transverse sectional area of the permanent magnet. When the magnetizing force is applied for magnetization after the permanent magnet before magnetized has been incorporated in the iron core, therefore, much magnetic flux flows into the iron core, and the permanent magnet is not sufficiently magnetized as desired. To solve this inconvenience, the permanent magnet after magnetized must be mounted on the iron core, requiring a cumbersome assembling operation. Besides, due to the constitution in which the permanent magnet is mounted on a portion of the outer peripheral edge of the iron core in the circumferential direction, the permanent magnet cannot be formed in a simple transverse sectional shape such as a circular shape or a rectangular shape. Moreover, it is relatively difficult to form a groove in the outer periphery of the iron core, resulting in increase in the manufacture cost. In the above composite magnet, further, the permanent magnet which is a relatively long requires an increased cost for the material.
Typical examples of the eddy current retarder using a permanent magnet include the one in which a magnet support cylinder having plural permanent magnets arranged in the outer peripheral surface thereof is moved into or out of the brake drum to make a changeover between braking and non-braking (see Japanese Laid-open Patent Application (Kokai) No. 14782/1994 (JP-A 6-14782)) and the one in which a magnet support cylinder having plural permanent magnets arranged in the outer peripheral surface thereof is rotated forward or reverse inside the brake drum to make a changeover between braking and non-braking (see Japanese Laid-open Patent Application (Kokai) No. 83571/1994 (JP-A 6-83571))(both of these applications were developed and filed by Isuzu Motor Co.). These eddy current retarders require an actuator for moving the magnet support cylinder. As the actuator, there can be employed a pneumatic cylinder, a hydraulic cylinder, an electric motor or a linear motor. Therefore, the device as a whole becomes of larger size and heavy in weight and increases cost. In the eddy current retarder using an electromagnet (see Japanese Laid-open Patent Application (Kokai) No. 327227/1994 (JP-A 6-327227)), on the other hand, there is no need of moving the electromagnet; i.e., applying the brake and not applying the brake can be changed over by simply controlling the electric current supplied to the coil of the electromagnet and hence, the above-mentioned actuator is not required. However, the device becomes considerably large sized and heavy, compared with the eddy current retarder using the permanent magnet.
Japanese Laid-open Patent Application (Kokai) No. 243627/1998 (JP-A 10-243627) that was developed and filed by Isuzu Motor Co. Ltd. discloses an eddy current retarder in which a brake drum is equipped with annular members made of a good conductor such as copper, a copper alloy or the like. The eddy current retarder includes a brake drum coupled to a rotary shaft and a stationary guide cylinder arranged on the inside of the brake drum in the radial direction. The stationary guide cylinder formed chiefly of a nonmagnetic material constitutes a nearly rectangular inner space inclusive of an outer wall surface and an inner wall surface. Plural ferromagnetic plates are arranged at intervals on the outer peripheral wall of the stationary guide cylinder that is so disposed, maintaining a gap, as to be opposed to the inner peripheral surface of the brake drum. In the inner space of the stationary guide cylinder is supported a magnet support cylinder so as to be moved in the axial direction by the actuator. Plural permanent magnets are arranged on the outer peripheral portion of the magnet support cylinder at intervals in the circumferential direction so as to be opposed to the ferromagnetic plates. Magnetic pole surfaces of the permanent magnets are directed in the radial direction, and the permanent magnets neighboring in the circumferential direction are so disposed that each of the magnetic pole surfaces has an opposite polarity to each other. An annular member made of a good conductor such as copper or a copper alloy is coupled to at least one end of the inner peripheral edge of the brake drum in the axial direction. The magnet support cylinder is selectively brought by the actuator to a braking position where the permanent magnets are opposed to the ferromagnetic plates arranged on the outer peripheral wall of the stationary guide cylinder on the inside of the brake drum in the radial direction and to a non-braking position where the permanent magnets are retracted outward in the axial direction from the inside of the brake drum in the radial direction and from the ferromagnetic plates.
When the brake drum being formed of an iron or a steel having a relatively large magnetic permeability and the magnet support cylinder is brought to the braking position by the actuator, a magnetic circuit is formed between the permanent magnets neighboring on the magnet support cylinder in the circumferential direction and the brake drum, via the ferromagnetic plates of the stationary guide cylinder. At this moment, a braking force is produced in the brake drum due to an eddy current that generates in the rotary brake drum. As described above, since the annular member made of a good conductor such as copper or a copper alloy, i.e., the annular member made of a material having a high electric conductivity is coupled to at least one end of the inner peripheral edge of the brake drum in the axial direction, an eddy current that generates increases and a braking force increases due to a combined action with that of the brake drum made of a material having a large permeability.
However, when the annular member made of a good conductor such as copper or a copper alloy is coupled to at least one end of the inner peripheral edge of the brake drum in the axial direction, there is a likelihood that the eddy current may concentrate in the annular member to make the annular member and the brake drum a high temperature. The electric resistance increases with an increase in the temperature of the annular member and of the brake drum, whereby the eddy current that generates in the brake drum decreases and hence, the braking force decreases. It is further probable that heat-deterioration of the annular member that works to increase the eddy current is promoted, whereby the braking force decreases and, besides, the annular member loses durability. Further, the copper member constituting the annular member has a coefficient of thermal expansion larger than that of the iron material or the steel material constituting the brake drum and hence, there is a probability that the junction portion between the annular member and the brake drum may peel off or may be cracked to spoil the durability. Besides, in case the brake drum is thermally expanded excessively, the thermal stress greatly increases in the annular member. When the centrifugal force is repetitively exerted in a state where the brake drum is revolving at high speeds, therefore, there is a probability that the junction portion between the annular member and the brake drum may be peeled off or cracked to spoil the durability.
An object of the present invention is to provide a novel composite magnet of electromagnet and permanent magnet, which makes it possible to effectively use both of the electromagnet and the permanent magnet.
Another object of the present invention is to provide a novel composite magnet of electromagnet and permanent magnet, which enables the length of the electromagnet in the direction of magnetization to be shortened compared to the length of the conventional counterpart, when it is supposed that the magnetic flux generated from one magnetic pole surface at the time of supplying a current to a coil is the same as that of the conventional counterpart.
A further object of the present invention is to provide a novel composite magnet of electromagnet and permanent magnet, which enables the whole constitution to be made in a compact size and in a decreased weight, and enables the production cost to be decreased.
A still further object of the present invention is to provide a novel composite magnet of electromagnet and permanent magnet, which enables the permanent magnet to be magnetized to a sufficient degree as desired after the permanent magnet before magnetized has been incorporated in the iron core, facilitating the operation for assembling the permanent magnet in the iron core.
A yet further object of the present invention is to provide a novel composite magnet of electromagnet and permanent magnet, which enables the permanent magnet to be formed in a simple shape in cross section and enables the composite magnet to be produced at a relatively low cost without requiring the formation of grooves in a portion of the outer periphery of the iron core in the circumferential direction.
A further object of the present invention is to provide a novel composite magnet of electromagnet and permanent magnet, which is capable of changing over between braking and non-braking as well as controlling the braking force by simply controlling the current flowing into the coil without using actuator and further enables the eddy current retarders to be made in a small size and in a reduced weight, compared to the conventional eddy current retarders utilizing the electromagnets.
Another object of the present invention is to provide a novel composite magnet of electromagnet and permanent magnet, which enables an amount of an eddy current generated in the brake drum and a braking torque to be increased by preventing the annular member and the brake drum from being heated at high temperatures.
A further object of the present invention is to provide a novel composite magnet of electromagnet and permanent magnet, which makes it possible to secure a desired durability to a sufficient degree.
According to one aspect of the present invention, there is provided a composite magnet of electromagnet and permanent magnet comprising an iron core, a coil arranged to surround the outer peripheral surface of the iron core, and a permanent magnet mounted in the iron core in a manner that the magnetic pole is in agreement with the direction of magnetization of the iron core, wherein the permanent magnet is mounted in a number of one or in a plural number in the iron core in a manner that at least the outer peripheral surfaces thereof are surrounded by the iron core.
It is desired that the permanent magnet is mounted in one end portion and/or in the other end portion of the iron core in the direction of magnetization.
It is desired that the end surface of the permanent magnet mounted in one end portion and/or the other end portion of the iron core in the direction of magnetization on the side same as the one end and/or the other end of the iron core is covered with a magnetic pole plate attached to one end and/or the other end of the iron core.
It is desired that the iron core is divided into two at an intermediate portion thereof in the direction of magnetization along the transverse cross section and that the permanent magnet is mounted across the ends of the iron cores facing each other.
It is desired that a magnetic pole portion is formed as a unitary structure at the other end of the iron core so as to extend outward in the radial direction or a magnetic pole plate is attached thereto.
It is desired that a through hole extending in the direction of magnetization is formed in the iron core, a permanent magnet is disposed at one end portion and/or the other end portion or in the intermediate portion of the through hole, a bar member made of a ferromagnetic material is disposed in the through hole in a region other than the region where the permanent magnet is disposed, magnetic pole plates are attached to the one end and to the other end of the iron core, and a nonmagnetic region is formed between the outer peripheral surfaces of the permanent magnet and of the bar member and the inner peripheral surface of the through hole over substantially the whole region in the axial direction.
It is desired that a one end-closed hole extending in the direction of magnetization is formed in the iron core, one end of said one end-closed hole being open at one end of the iron core and being closed at the other end, a permanent magnet is disposed in the open end of the one end-closed hole, a bar member made of a ferromagnetic material is disposed in the one end-closed hole in a region other than the region where the permanent magnet is disposed, a magnetic pole plate is attached to the one end of the iron core, a magnetic pole portion is formed as a unitary structure on the other end of the iron core so as to protrude outward in the radial direction or a magnetic pole plate is attached thereto, and a non-magnetic region is formed between the outer peripheral surfaces of the permanent magnet and of the bar member and the inner peripheral surface of the one end-closed hole over substantially the whole region in the axial direction.
It is desired that the nonmagnetic region is formed by a cylindrical hollow portion formed over the whole region in the axial direction, or formed by a cylindrical hollow portion formed in part of the region in the axial direction and nonmagnetic hollow member inserted in other region, or formed by a nonmagnetic hollow member inserted in the whole region in the axial direction.
It is desired that a recessed portion is formed in one inner side surface and/or the other inner side surface of the magnetic pole plate, the one end of the permanent magnet disposed in one end portion and/or the other end portion of the through hole, which includes one magnetic pole surface, is fitted into the recessed portion, another recessed portion is formed in the other magnetic pole surface of the permanent magnet, a protruded portion is formed on one end surface and/or the other end surface of the bar member, and said protruded portion of the bar member is fitted into said another recessed portion of the permanent magnet.
It is desired that a through hole extending in the direction of magnetization is formed in the iron core, a permanent magnet is disposed in one end of the through hole, a bar member made of a ferromagnetic material is disposed in the through hole in a region other than the region where the permanent magnet is disposed, magnetic pole plates are attached to the one end and to the other end of the iron core, a nonmagnetic region is formed between the outer peripheral surfaces of the permanent magnet and of the bar member and the inner peripheral surface of the through hole over substantially the whole region in the axial direction, a recessed portion is formed in the other magnetic pole plate, and the end of the bar member on the other side of the magnetic pole plate is fitted to the recessed portion.
It is desired that the through hole in the iron core has a large diameter portion formed at one end thereof, a nonmagnetic hollow member is fitted to the large diameter portion, the permanent magnet is fitted to the one end portion of the nonmagnetic hollow member, an end of the bar member is fitted to the other end portion of the nonmagnetic hollow member, and a cylindrical hollow portion is formed between the outer peripheral surface of the bar member of the remaining region excluding the one end portion thereof and the corresponding inner peripheral surface of the through hole.
It is desired that the one end-closed hole in the iron core has a large diameter portion formed at one end thereof, a nonmagnetic hollow member is fitted to the large diameter portion, the permanent magnet is fitted to the one end portion side of the nonmagnetic hollow member, an end of the bar member is fitted to the other end portion side of the nonmagnetic hollow member, and a cylindrical hollow portion is formed between the outer peripheral surface of the bar member of the remaining region excluding the one end portion thereof and the corresponding inner peripheral surface of the through hole.
It is desired that the amount of magnetic flux generated by the permanent magnet is nearly equal to the amount of magnetic flux generated by the coil, or the amount of the magnetic flux generated by the coil is defined to be larger, and the transverse sectional area of the iron core of a portion on which the permanent magnet is mounted is defined to be saturated with the magnetic flux of the magnetic field generated by the coil.
According to another aspect of the present invention, there is provided an eddy current retarder comprising a brake drum coupled to a rotary shaft, and a stationary magnet unit disposed on the inside of the brake drum in the radial direction, the stationary magnet unit including:
an annular base portion;
plural iron core portions extending outward in the radial direction from the outer peripheral edge of the base portion at intervals in the circumferential direction;
a support member having magnetic pole pieces arranged at the ends of the iron core portions so as to be opposed to the inner peripheral surface of the brake drum;
electromagnets formed by the iron core portions and the coils arranged to cover the outer peripheral surfaces of the iron core portions; and
at least one permanent magnet buried in each of the iron core portions with the magnetic pole surface being directed in the radial direction; and
an electric current being supplied to the coils to produce in the brake drum a braking force based on an eddy current generated by a magnetic field produced by the electromagnets and the corresponding permanent magnets.
It is desired that the support member is formed by laminating plural electromagnetic steel plates in the axial direction or by laminating plural blocks in the axial direction.
It is desired that the support member is formed by laminating, in the axial direction, plural electromagnetic steel plates that are divided in the circumferential direction, or by stacking, in the axial direction, plural blocks that are divided in the circumferential direction.
It is desired that the support member is formed by laminating plural electromagnetic steel plates in the axial direction, and a reinforcing plate having substantially the same shape as the electromagnetic steel plates in transverse cross section is superposed on at least the one end surface of the support member in the axial direction.
It is desired that provision is made of a stationary frame having annular support plates so disposed that the direction of thickness is in agreement with the axial direction, and the stationary magnet unit and the base portions of the reinforcing plates are superposed on the support plate portion of the stationary frame and these are fastened as a unitary structure by bolts or rivets.
It is desired that annular members formed of a good conductor such as copper, a copper alloy or the like are disposed on the inner peripheral surfaces and/or on the end surfaces of the brake drum.
According to a further aspect of the present invention, there is provided an eddy current retarder comprising a brake drum coupled to a rotary shaft and a stationary magnet unit disposed on the inside of the brake drum in the radial direction, the stationary magnet unit including:
an annular stationary support cylinder;
plural iron cores arranged on the outer peripheral edge of the stationary support cylinder at intervals in the circumferential direction;
magnetic pole plates disposed at the ends of the iron cores so as to be opposed to the inner peripheral surface of the brake drum;
electromagnets formed by the iron cores and by coils arranged so as to cover the outer peripheral surfaces of the iron cores; and
at least one permanent magnet buried in each of the iron cores with the magnetic pole surface being directed in the radial direction; and
an electric current being supplied to the coils to produce in the brake drum a braking force based on an eddy current generated by a magnetic field due to the electromagnets and the corresponding permanent magnets.
According to a still further aspect of the present invention, there is provided an eddy current retarder comprising a pair of brake disks coupled to a rotary shaft at a distance in the axial direction and an annular stationary magnet unit disposed between the brake disks, the stationary magnet unit including:
an annular stationary support frame;
plural iron cores arranged on the stationary support frame at intervals in the circumferential direction;
magnetic pole plates disposed at the ends of the iron cores so as to be opposed to the inner side surfaces which are opposed to each other of the brake disks;
electromagnets formed by the iron cores and by coils disposed so as to cover the outer peripheral surfaces of the iron cores; and
at least one permanent magnet buried in each of the iron cores with the magnetic pole surface being directed in the radial direction; and
an electric current being supplied to the coils to produce in the brake disks a braking force based on an eddy current generated by a magnetic field due to the electromagnets and the corresponding permanent magnets.
According to a yet further aspect of the present invention, there is provided an eddy current retarder comprising a stationary brake drum, an annular magnet support member that is coupled to the rotary shaft and is disposed on the inside of the stationary brake drum in the radial direction, and plural magnets disposed on the outer periphery of the magnet support member at intervals in the circumferential direction so as to be opposed to the inner peripheral surface of the stationary brake drum, said eddy current retarder further comprising:
annular members formed of a good conductor such as copper or a copper alloy coupled to the inner peripheral edges and/or to the ends in the axial direction of the stationary brake drum; and
a liquid chamber disposed in the stationary brake drum for circulating the cooling liquid;
wherein the liquid chamber is partly close to, or in contact with, the annular members.
It is desired that the stationary brake drum has an inner peripheral wall opposed to the outer periphery of the magnet support member, the annular members are coupled to at least the end portions in the axial direction of the inner peripheral wall, and the end portions of the inner peripheral wall to which the annular member are coupled have a thickness smaller than the thickness of the inner peripheral wall of other portions.
It is desired that the magnet disposed on the magnet support member is constituted by:
an electromagnet which includes iron cores disposed on the outer periphery of the magnet support member at a distance in the circumferential direction, coils disposed so as to cover the outer peripheral surfaces of the iron cores, and magnetic pole pieces disposed at the ends of the iron cores so as to be opposed to the inner peripheral surface of the stationary brake drum; or
a composite magnet constituted by the electromagnet and permanent magnets buried in the iron cores of the electromagnet.
It is desired that the surfaces of the peripheral edges of each magnetic pole piece of the magnet, which is opposed to the inner peripheral surface of the stationary brake drum, are so inclined that the distance between said surfaces and the inner peripheral surface of the stationary brake drum gradually increases toward the peripheral edges of the magnetic pole piece.
According to another aspect of the present invention, there is provided an eddy current retarder comprising a magnet support cylinder coupled to the rotary shaft, a stationary brake drum disposed on the inside of the magnet support cylinder in the radial direction, and plural magnets disposed on the inner periphery of the magnet support cylinder in the circumferential direction at intervals so as to be opposed to the outer peripheral surface of the stationary brake drum, said eddy current retarder further comprising:
annular members formed of a good conductor such as copper or a copper alloy coupled to the outer peripheral edges and/or to the ends in the axial direction of the stationary brake drum; and
a liquid chamber disposed in the stationary brake drum for circulating the cooling liquid;
wherein the liquid chamber is partly close to, or in contact with, the annular members.
It is desired that the stationary brake drum has an outer peripheral wall opposed to the inner periphery of the magnet support cylinder, the annular members are coupled to at least the end portions in the axial direction of the outer peripheral wall, and the end portions of the outer peripheral wall to which the annular member are coupled have a thickness smaller than the thickness of the outer peripheral wall of other portions.
It is desired that the magnet disposed on the magnet support member is constituted by:
an electromagnet which includes iron cores disposed on the inner periphery of the magnet support cylinder at a distance in the circumferential direction, coils disposed so as to cover the outer peripheral surfaces of the iron cores, and magnetic pole pieces disposed at the ends of the iron cores so as to be opposed to the outer peripheral surface of the stationary brake drum; or
a composite magnet constituted by the electromagnet and permanent magnets buried in the iron cores of the electromagnet.
It is desired that the surfaces of the peripheral edges of each magnetic pole piece of the magnet, which is opposed to the outer peripheral surface of the stationary brake drum, are so inclined that the distance between said surfaces and the outer peripheral surface of the stationary brake drum gradually increases toward the peripheral edges of the magnetic pole piece.